1. Field of the Invention
The invention relates to a mobile communication terminal and a method of accomplishing transmission power control (TPC) in a mobile communication terminal.
2. Description of the Related Art
In a W-CDMA (Wideband Code Division Multiple Access) system which have been recently popularly used in a wireless communication system, since a common frequency is used in all channels, communication channel is frequently interfered with other communication channels. A channel capacity is dependent highly on such interferences.
From a standpoint of a channel capacity, it is preferable to minimize transmission power by which a base station transmits data to a mobile communication terminal, in order to increase channel capacity.
However, if such transmission power is mandatorily reduced, there is caused problems of reduction in a calling success rate and necessity of repeatedly transmitting data.
In order to avoid such problems, for instance, Japanese Patent Application Publication No. 09-009352 has suggested a mobile communication terminal which controls an amplification level of transmission power by which the mobile communication terminal transmits a signal to a base station. Specifically, the transmission power is increased only in a predetermined period of time, ensuring a high efficiency at which the mobile communication can receives a call from a base station, with reduction in power consumption.
However, the suggested mobile communication terminal is directed only to control in transmission power by which the mobile communication terminal transmits a signal to a base station, but is not directed to control in transmission power by which a base station transmits a signal to the mobile communication terminal.
Communication quality in a mobile communication terminal is dependent on a SIR (Signal to Interference Ratio) defined as a ratio of power of an interference signal to power of a received signal. Accordingly, even if a base station transmits a signal to a mobile communication terminal with much power, communication quality would be deteriorated, if power of an interference signal is also high. Thus, it is not always to be able to provide desired communication quality, only if control is accomplished to an amplification level of power by which the mobile communication terminal transmits a signal to a base station.
In addition, the above-mentioned related mobile communication terminal is accompanied with a problem that a high target SIR causes a high load to a channel capacity in a mobile network, resulting in reduction in a number of mobile communication terminals covered by a base station.
On the other hand, a small target SIR causes a problem of failure in establishment in communication between a base station and a mobile communication terminal, and extension in time necessary for establishment in communication between a base station and a mobile communication terminal, caused by repetition in transmission of DCCH (Dedicated Control CHannel) data acting as a calling signal.
In view of the above-mentioned problems in the related mobile communication terminal, it is an object of the present invention to provide a mobile communication terminal which is capable of reducing a load to a channel capacity in a mobile network, and preventing deterioration in a calling success rate.
It is also an object of the present invention to provide a method of accomplishing transmission power control in a mobile communication terminal, which is capable of doing the same.
It is further an object of the present invention to provide a program for causing a computer to carry out the above-mentioned method.